[RFC PATCH v2 4/6] KVM: x86: Introduce fault type to indicate kvm page fault is private
From: isaku . yamahata
Date: Thu Jun 22 2023 - 19:17:43 EST
From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
Introduce kvm fault type to indicate how to handle kvm page fault.
It is unfortunate and inflexible for kvm_mmu_do_page_fault() to call
kvm_mem_is_private(), eventually looking up memory attributes. Later
__kvm_faultin_pfn() looks up memory attributes again. There is a race
condition that other threads can change memory attributes due to not
gaining the mmu lock. SNP-SEV and TDX define theri way to indicate that
the page fault is private.
Add KVM fault type, add mmu_private_fault_mask to struct kvm_arch for SNP
to determine the fault is private, add gfn_shared_mask to struct kvm_arch
for TDX to determine the fault is private. KVM_FAULT_SHARED_ALWAYS is added
for the conventional guest to avoid over head to lookup memory attributes.
Suggested-by: Michael Roth <michael.roth@xxxxxxx>
Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
---
Changes v1 -> v2:
- Introduced fault type and replaced is_private with fault_type.
- Add kvm_get_fault_type() to encapsulate the difference.
---
arch/x86/include/asm/kvm_host.h | 6 ++++++
arch/x86/kvm/mmu/mmu.c | 26 ++++++++++++++++++++------
arch/x86/kvm/mmu/mmu_internal.h | 33 +++++++++++++++++++++++++++++++--
3 files changed, 57 insertions(+), 8 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 8ae131dc645d..5afeefc7a516 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1445,6 +1445,12 @@ struct kvm_arch {
*/
#define SPLIT_DESC_CACHE_MIN_NR_OBJECTS (SPTE_ENT_PER_PAGE + 1)
struct kvm_mmu_memory_cache split_desc_cache;
+
+#ifdef CONFIG_KVM_PROTECTED_VM
+ /* To make the patch compile. */
+ u64 mmu_private_fault_mask;
+ gfn_t gfn_shared_mask;
+#endif
};
struct kvm_vm_stat {
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index b8ba7f11c3cb..feec75515f39 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3174,10 +3174,12 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn,
static int __kvm_mmu_max_mapping_level(struct kvm *kvm,
const struct kvm_memory_slot *slot,
- gfn_t gfn, int max_level, bool is_private)
+ gfn_t gfn, int max_level,
+ enum kvm_fault_type fault_type)
{
struct kvm_lpage_info *linfo;
int host_level;
+ bool is_private = fault_type == KVM_FAULT_PRIVATE;
max_level = min(max_level, max_huge_page_level);
for ( ; max_level > PG_LEVEL_4K; max_level--) {
@@ -3228,7 +3230,7 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
*/
fault->req_level = __kvm_mmu_max_mapping_level(vcpu->kvm, slot,
fault->gfn, fault->max_level,
- fault->is_private);
+ fault->fault_type);
if (fault->req_level == PG_LEVEL_4K || fault->huge_page_disallowed)
return;
@@ -4328,7 +4330,7 @@ static int kvm_do_memory_fault_exit(struct kvm_vcpu *vcpu,
struct kvm_page_fault *fault)
{
vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
- if (fault->is_private)
+ if (fault->fault_type == KVM_FAULT_PRIVATE)
vcpu->run->memory.flags = KVM_MEMORY_EXIT_FLAG_PRIVATE;
else
vcpu->run->memory.flags = 0;
@@ -4386,10 +4388,22 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
return RET_PF_EMULATE;
}
- if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn))
- return kvm_do_memory_fault_exit(vcpu, fault);
+ if (fault->fault_type == KVM_FAULT_SHARED_ALWAYS) {
+ /*
+ * The conventional case. Don't lookup memory attributes to
+ * avoid overhead
+ */
+ fault->fault_type = KVM_FAULT_SHARED;
+ } else if (fault->fault_type == KVM_FAULT_MEM_ATTR) {
+ fault->fault_type = kvm_mem_is_private(vcpu->kvm, fault->gfn) ?
+ KVM_FAULT_PRIVATE : KVM_FAULT_SHARED;
+ } else {
+ if ((fault->fault_type == KVM_FAULT_PRIVATE) !=
+ kvm_mem_is_private(vcpu->kvm, fault->gfn))
+ return kvm_do_memory_fault_exit(vcpu, fault);
+ }
- if (fault->is_private)
+ if (fault->fault_type == KVM_FAULT_PRIVATE)
return kvm_faultin_pfn_private(vcpu, fault);
async = false;
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 7f9ec1e5b136..0ec0b927a391 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -188,6 +188,13 @@ static inline bool is_nx_huge_page_enabled(struct kvm *kvm)
return READ_ONCE(nx_huge_pages) && !kvm->arch.disable_nx_huge_pages;
}
+enum kvm_fault_type {
+ KVM_FAULT_MEM_ATTR,
+ KVM_FAULT_SHARED,
+ KVM_FAULT_SHARED_ALWAYS,
+ KVM_FAULT_PRIVATE,
+};
+
struct kvm_page_fault {
/* arguments to kvm_mmu_do_page_fault. */
const gpa_t addr;
@@ -203,9 +210,10 @@ struct kvm_page_fault {
/* Derived from mmu and global state. */
const bool is_tdp;
- const bool is_private;
const bool nx_huge_page_workaround_enabled;
+ enum kvm_fault_type fault_type;
+
/*
* Whether a >4KB mapping can be created or is forbidden due to NX
* hugepages.
@@ -282,6 +290,27 @@ enum {
RET_PF_SPURIOUS,
};
+static inline enum kvm_fault_type kvm_get_fault_type(struct kvm *kvm,
+ gpa_t gpa, u64 err)
+{
+
+#ifdef CONFIG_KVM_PROTECTED_VM
+ /* SEV-SNP handling */
+ if (kvm->arch.mmu_private_fault_mask)
+ return (err & kvm->arch.mmu_private_fault_mask) ?
+ KVM_FAULT_PRIVATE : KVM_FAULT_SHARED;
+
+ /* TDX handling */
+ if (kvm->arch.gfn_shared_mask)
+ return (gpa_to_gfn(gpa) & kvm->arch.gfn_shared_mask) ?
+ KVM_FAULT_SHARED : KVM_FAULT_PRIVATE;
+#endif
+ if (kvm->arch.vm_type == KVM_X86_PROTECTED_VM)
+ return KVM_FAULT_MEM_ATTR;
+ /* Don't query memory attributes. */
+ return KVM_FAULT_SHARED_ALWAYS;
+}
+
static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
u64 err, bool prefetch, int *emulation_type)
{
@@ -301,7 +330,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
.max_level = KVM_MAX_HUGEPAGE_LEVEL,
.req_level = PG_LEVEL_4K,
.goal_level = PG_LEVEL_4K,
- .is_private = kvm_mem_is_private(vcpu->kvm, cr2_or_gpa >> PAGE_SHIFT),
+ .fault_type = kvm_get_fault_type(vcpu->kvm, cr2_or_gpa, err),
};
int r;
--
2.25.1